Astronomers hatch plan to move Earth's orbit from warming sun

(CNN) -- A group of astronomers has come up with a plan they claim will save life on Earth from an early demise. All it takes, they say, is moving the planet into a different orbit.

Their deadline is about 3.5 billion years in the future. At that time, the scientists say, the sun will be 40 percent brighter than it is today and the Earth will be too hot to sustain life. Even looking just a billion years down the road, the increased brightness of the sun would cause a "moist greenhouse" effect which will have a catastrophic impact on the planet.

But what if the Earth could be moved farther away from the sun before it gets too hot for human life?

Researchers Don Korycansky of the University of California-Santa Cruz, Gregory Laughlin of NASA, and Fred Adams of the University of Michigan say the idea of changing the Earth's orbit is almost, "alarmingly feasible."

The scientists' theory is outlined in a paper entitled "Astronomical engineering: A strategy for modifying planetary orbit." The paper has been accepted for publication in the journal "Astrophysics and Space Science."

The researchers' theory is a twist on the "gravity-assist" technique used to send spacecraft to the outer planets. The team says that by shooting a large object (such as an asteroid about 62 miles across) past the Earth, the planet could be gradually pulled away from the Sun. It would take thousands of encounters to make a difference. One million encounters would move the Earth out 41 million miles, or about 50 percent farther from the sun than it is today.

But the researchers say that if the technique is repeated an average of every 6,000 years, the orbit could be increased to keep pace with the Sun's increasing brightness. The result, they say, would be to keep the Earth habitable for up to an extra 5 billion years.

The scientists say their plan is not without some drawbacks. In order for this method to work, the asteroid would have to pass by Earth within about 10,000 miles. If the asteroid comes too close, it might break up or conceivably even slam into Earth.

Another possible side effect of shooting such a large object past Earth, the scientists say, would be to increase the planet's rotation. The encounters would have to be planned so that while some would cause the Earth to spin faster, others would slow it down back to normal rotation speed. It's also possible that the moon would be thrown from its orbit around the Earth during these fly-bys.